Occasionally, it is desired to increase the piston rod output force in a cylinder while utilizing a single existing power source to the piston. Of particular interest is where the power source is a pneumatic or hydraulic power source. At the present time, this is accomplished by providing a power supply that is exterior to the cylinder body using multiple ports and exhausts mounted thereon. Control valves and manifolds are required in such a structure. Examples of this are shown in U.S. Pat. Nos. 3,288,036 Fisher and 3,880,051 Eppler. Such devices are complex and expensive. Furthermore, for applications such as handheld tools, the outside contour of such devices makes them inapplicable for such use due to external valving and piping. Also, equal force is not provided to all pistons simultaneously.
Attempts have been made to eliminate the complex control valves and manifolds but the results have been complex, expensive multi-piece designs where the pistons are all mounted on one rod and there is an internal manifold. Examples of these are U.S. Pat. Nos. 3,430,539 Freeman; 3,485,141 Ott, et al.; and 3,457,840 Grimes.